Hydrophobizing agents are widely used as water repellent materials to impart water resistance to such compositions as textiles, carpet fibers, paper and paperboard, when applied thereon. Many materials are known in the art to be useful as hydrophobizing agents for water repellency applications including organometallic complexes, waxes and wax-metal emulsions, resin-based finishes, silicones, rosin, hexadecylketene dimers, and fluoro chemicals, to name a few. A general review of the many types of water repellent chemicals useful as hydrophobizing agents is provided by M. Hayek in the Encyclopedia of Chemical Technology, Volume 24, (1984), "Waterproofing and Water/Oil Repellency" pages 442 through 465, and is incorporated herein by reference.
It is well known in the art that many hydrophobizing agents can be stabilized in aqueous dispersion form by the presence of surfactants, usually fatty acid salts, or salts of sulfated fatty alcohols, in order to facilitate their handling and application onto materials, especially at surfaces or at interfaces, for the purpose of imparting water repellency. Such dispersions typically contain relatively high concentrations of surfactant and/or protective colloids as dispersion stabilizers, typically greater than 10% by weight based on hydrophobizing agent, the presence of which surfactants or protective colloid dispersion stabilizers, while providing the necessary colloidal stability for practical preparation of such aqueous dispersions, and while providing the necessary surface activity to ensure deposition of the hydrophobizing agent at surfaces or interfaces, detracts from the repellency properties desired upon final application. This results from the presence of the usually hygroscopic surfactant or protective colloid dispersion stabilizer in the resulting water repellent layer, which promotes aqueous rewetting and swelling of the deposited hydrophobizing agent. In the case of reactive hydrophobizing agents such as fatty acid anhydrides, hexadecylketene dimer, and alkenylsuccinic anhydrides, capable of forming covalent bonds with active hydrogen-containing substrates, the high levels of dispersion stabilizers required for colloidal stability can further interfere with the covalent reactions anchoring the repellent to the substrate, by competing with the substrate for active sites, in addition to the aforementioned rewetting phenomenon. In the case of hydrophobizing agents comprising crystalline waxy materials, such as those selected from the group comprising the various natural, mineral, and synthetic waxes, alkylketene dimers, such as hexadecylketene dimer, and fatty triglycerides such as tristearin or castor wax, or blends of crystalline materials, with themselves or with amorphous hydrophobizing agents, substantially higher levels of dispersion stabilizer are frequently required to offset the pronounced negative effect the crystalline nature of the hydrophobizing agent has on dispersion stability. Indeed, attempts to incorporate even low levels of crystalline materials into aqueous dispersions frequently causes an aqueous dispersion of amorphous hydrophobizing agent to gel upon standing. Thus shipping, storage, and handling requirements require that high levels of dispersion stabilizer be used to ensure sufficient colloidal stability to prevent dispersion flocculation, viscosity build, and eventual gelation or solidification, rendering the dispersion less suitable for practical water repellent applications. Nevertheless, crystalline materials provide a high degree of water repellency and it is frequently a goal of manufacturers of hydrophobizing agent dispersions to blend crystalline materials with less costly amorphous materials to achieve a proper balance of economics and high performance. It is therefore desirable to minimize the presence of dispersion stabilizing additives, such as surfactants or protective colloids, in the final water repellent hydrophobizing agent dispersion, in order to achieve the greatest efficiency of active ingredient utilization.
One method for providing such colloidal stability, in addition to the aforementioned use of high levels of surfactants, has been to prepare the dispersions in relatively dilute form, usually less than 10% to 20%, by weight based on total dispersion, of hydrophobizing agent. While this may provide sufficient stability for many applications, it can also lead to inefficiencies in storage and shipping since the quantity of inactive ingredient, water, becomes excessively large, requiring surplus storage facilities and shipping containers for what amounts to low levels of useful or active ingredient. It is therefore also desirable to maximize the concentration of hydrophobizing agent in the dispersion, to provide the greatest efficiency of storage and least costly method of transport.
One attempt to overcome the disadvantages that high levels of surfactants bring to aqueous wax emulsions is described in U.S. Pat. No. 3,432,319, which discloses paraffin wax emulsion compositions comprising relatively low concentrations of a hydroxyalkyl methylcellulose ether dispersion stabilizer. Several advantages associated with the absence of conventional surfactants and the use of high aqueous concentrations of wax are disclosed including increased mechanical shear stability and increased comparability with urea-formaldehyde resins. However the hydrophobizing wax material is restricted to paraffin wax. Indeed, in contrast to the instant invention, partial or complete substitution of the paraffin wax with crystalline or waxy non-reactive hydrophobic materials, such as beeswax or tristearin, or crystalline reactive waxy materials, such as hexadecylketene dimer, according to said patent, renders the mixtures unemulsifyable or results in dispersions of very limited storage stability. Thus the benefit of the dispersions as disclosed is restricted to those consisting of paraffin waxes.
One attempt at improving the colloidal stability, for storage and handling purposes, of dispersions containing crystalline hydrophobizing agents is disclosed in U.S. Pat. No. 4 296 012 which describes the requirements of utilizing a non-crystalline hydrocarbon resin in combination with a crystalline ketene dimer in order to achieve the appropriate amount of stability in the ketene dimer dispersion, while providing a high degree of sizing effect. However, the dispersions are relatively dilute, typically 15% by weight of total dispersion of non-volatile component and contain a high concentration of dispersion stabilizer, typically greater than 20% by weight based on concentration of hydrophobizing agent. In contrast, the dispersions of the instant invention are stable in the presence of crystalline materials alone, even at concentrations of hydrophobizing agent up to about 40% by weight of total dispersion.
A combination of a cationic dispersing agent and alkyl hydroxyalkyl cellulose, as dispersion stabilizers for substituted ketene dimer dispersions, is disclosed in U.S. Pat. No. 3,931,069. The dispersions are useful for sizing cellulose fibers and contain up to 30%, by weight, of total solids content. However the total solids content represents the combined concentrations of the ketene dimer and the stabilizers, making the highest attainable solids content of the ketene dimer, based on weight of total dispersion, significantly less than 30%. In contrast, the dispersions of the instant invention readily achieve hydrophobizing agent concentrations in excess of 35% to 40% by weight of total dispersion.
Furthermore, it had been disclosed and claimed in U.S. Pat. No. 2,627,477 aqueous emulsions of higher ketene dimers, containing a water-soluble cellulose ether, useful in sizing paper. However the examples teach that very high levels of water-soluble cellulose ether relative to ketene dimer, up to as much as 300% by weight of stabilizer based on ketene dimer or greater, are employed. The resulting dispersions themselves are very dilute, typically 0.5% by weight of ketene dimer based on total dispersion, and describe pre-dissolution of the dimer in an organic solvent. In contrast, the dispersions of the instant invention readily achieve a high degree of stability utilizing dispersions stabilizers at concentrations less than about 2%, by weight, based on hydrophobizing agent, and hydrophobizing agent concentrations up to about 40% by weight of total dispersion.
U.S. Pat. No. 5,013,775 discloses the difficulty associated with preparation of stable high concentration aqueous dispersion sizing agents based on ketene dimer compounds and suggests a solution whereby a composition comprising a hydrophilic copolymer polymerized in the presence of an alkylmercaptan is utilized to stabilize the hydrophobic ketene dimer compounds in aqueous dispersion form. The resulting dispersions are clearly distinguishable from the dispersions of the instant invention in that they typically contain about 20% by weight of ketene dimer of dispersion stabilizer, at total non-volatile solids of 20% by weight of total dispersion
U.S. Pat. No. 5,028,236 describes ketene dimer dispersions useful for the treatment of wool and synthetic polyamide fibers The dispersions of said invention are dilute, less than about 10%, by weight of total dispersion, of hydrophobizing agent, and utilize high levels of dispersion stabilizer, typically 8% by weight based on hydrophobizing agent.
Lastly, a detailed description of the complex considerations necessary in the design of stable industrial emulsions, including wax emulsions, is provided by W. C. Griffin, in the Encyclopedia of Chemical Technology, Volume 8, (1979), "Emulsions", pages 900 through 930. This reference discloses that wax emulsions, i.e. dispersions, may be stabilized against agglomeration by buffering with an organic ester, although no details are given.